[Pitch] Conform `Never` to `Codable`

[anon9791410]

This is a good pitch and it should be implemented. Thank you.

However,

1. I don't think it's important to make Void Codable, but I do think it's nonsensical for Never to be Codable otherwise, given that you can have a () instance. (This will take more work, and shouldn't hold up the easy addition for Never.)

@tkremenek

However, being a bottom type does not imply that Never should implicitly conform to all protocols. Instead, convenient protocol conformances for Never should be added as deemed useful or necessary.

If Never conformed to all protocols, it would be a useful constraint to virtually remove the genericism of outer types, similar to what @bbrk24 mentions above. I don't think it's possible to find a conformance that won't be useful, and would also cause harm by being implicit. But I'm also not going to read through that whole thread and I think there's a good chance someone in there might have proved me wrong.